Gear shifting transmissions of motor vehicles are usually controlled and/or shifted by means of an actuating device arranged within reach of the driver. Actuating elements such as shift levers or selector levers are regularly used for this purpose and are arranged, for example, between the front seats of the motor vehicle.
The design and ergonomic requirements for shift levers or selector levers of this type are manifold. For example, in order to convey a realistic sensation of operating the transmission to the driver, generic actuating devices require that the driver be provided with both optical and clear haptic or tactile feedback. Based on this, the driver is supposed to be able to deduce the occurred shifting process, and grasp the current shifting state of the transmission at a glance or by intuitively reaching for the selector lever.
In this context, it is therefore desirable to provide the driver with clear optical and haptic feedback about the current state of the transmission and/or engaged drive position by means of the respective current position or angular position of the selector lever.
In the case of a mechanical gear actuation system and/or mechanical coupling between the selector lever and the gear shifting transmission—for example by means of a control wire or linkage—the position of the selector lever always matches the actual gear setting owing to the mechanical coupling. Besides, since the gear positions are stable, the position of the selector levers is consequently also stable. As a result, on the one hand, the driver may ascertain the current shifting state of the transmission from the respective position of the selector lever and/or recognize the respectively engaged gear in the transmission from the position of the selector lever, and, on the other hand, he can be assured that the position of the selector lever never deviates from the actual shifting state of the transmission.
In the case of electrical actuation and/or shift-by-wire actuation of the gear shifting transmission, however, no mechanical coupling exists between the actuating element in the passenger compartment and the motor vehicle transmission. In the case of shift-by-wire transmissions, the shift commands are instead transmitted from the actuating device to the motor vehicle transmission exclusively by means of electric or electronic signals. This applies in part to modern manual transmissions, in particular, however, to modern generations of automatic transmissions, which usually are entirely remote-controlled by actuators.
In the case of the shift-by-wire actuated gear shifting transmissions, the missing mechanical connection between the transmission actuator system and the selector lever, however, may result in that the position of selector lever no longer matches the shifting state of the transmission under certain conditions or in the event of a malfunction.
Modern automatic transmissions, for example, generally have a so-called auto-P function, which ensures that on leaving the vehicle the parking lock is always engaged in the transmission in order to prevent the unattended vehicle from rolling away, for example. The auto-P function, which, for example, always occurs when the ignition key is removed or the vehicle is locked, in order words, ensures the automatic engagement of the parking lock independently of the drive position actually selected at the selector lever. By means of the auto-P function of the transmission and/or vehicle, the parking lock is thus also engaged if the driver, for example, in fact left the selector lever in the neutral position, or in one of the drive position settings.
In this case, however, the position of the selector lever no longer matches the actual shifting state of the transmission. When returning to the vehicle, or when starting the vehicle, the driver is thus provided with inaccurate optical as well as haptic information by the position of the selector lever. From observing the position of the selector lever, the driver assumes that the transmission is in the neutral position, or in a drive position setting, while the parking lock is in fact engaged in the transmission. This discrepancy between the position of the selector lever and the state of the transmission can thus result in undesirable operating errors, wrong conclusions by the driver, and consequently in safety-critical situations.
Attempts have been made to counteract the described problems by designing selector levers of shift-by-wire gear shifting transmissions as monostable actuating elements. In other words, this means that after each operation such a monostable selector lever always returns to the same center position. In the case of a monostable selector lever, the feedback on the actual shifting state of the transmission is thus exclusively left to a separate indicator, for example by means of light emitting diodes. In contrast, in a monostable selector lever the possibility of providing the driver with optical or haptic feedback on the shifting state of the transmission based on the position of the selector lever is omitted.
Monostable actuating devices have the additional disadvantage that the driver has to get used to a new operational concept of the lever continuously striving to return to the center position, this operational concept differing significantly from the traditional operation of the transmission.